1. Field of the Invention
The present invention relates to an additive for improving post exposure delay stability of a photoresist, and a composition comprising the same. In one particular aspect of the present invention, urea derivatives of the present invention are used as an additive in a chemically amplified photoresist composition that can efficiently prevent phenomena of lack of pattern formation and T-topping due to the post exposure delay (PED). PED is a disadvantage of alicyclic compounds used in the lithography process using light sources such as KrF (248 nm), ArF (193 nm), VUV (157 nm), E-beam, ion beam and EUV.
2. Description of the Background Art
Use of chemical amplification-type photoresists (i.e., photoresist compositions) is currently being investigated in photolithography processes using light source such as KrF, ArF, VUV and EUV to achieve a high sensitivity in minute image-formation on semiconductor devices. Such photoresists are generally prepared by blending a photoacid generator with a matrix resin polymer (i.e., photoresist polymer) having an acid labile group.
In a photolithography process for producing semiconductor devices, the resolution of an image depends on the wavelength of the light used. Thus, the shorter the wavelength, the higher the resolution, i.e., shorter wavelengths allow smaller pattern formation.
In order to be useful in a photolithography process, a photoresist (PR) must have an excellent etching resistance, heat resistance, and adhesiveness. Moreover, to reduce the cost of manufacturing semiconductor devices, a PR should be capable of being developed by a common developing solution, such as a 2.38 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. These qualities are particularly important in photolithography processes utilizing a deep ultraviolet light source (i.e., short wavelength light source), including KrF (248 nm), ArF (193 nm), VUV (157 nm) and EUV (13 nm).
While it is difficult to synthesize a photoresist polymer that satisfies all of these requirements, a variety of photoresist polymers with improved etching resistance, adhesiveness and resolution have been developed. Unfortunately, however, most chemically amplified photoresists currently available have a relatively short post exposure delay (PED) stability. In general, when there is delay between exposure of the photoresist to light and development of the exposed photoresist, acids that are generated on the exposed area are neutralized by amine compounds which may be present in the production atmosphere. Since the pattern formation depends on acids that are generated by the exposure, neutralization of acids by atmospheric amine compounds reduce, prevent or alter a pattern formation, e.g., a T-topping phenomenon may occur where the top portion of the pattern forms a T-shape. This problem is especially acute when the concentration of environmental amine is over 30 ppb, which leads to no pattern formation.
In theory, one may overcome the aforementioned disadvantages by improving the photoresist polymer or by adding an additive to improve the PED stability of the photoresist composition. In the conventional art, various amine compounds, in particular, amine compounds that are weakly basic and/or have bulky groups, have been employed as additives to increase the PED stability. However, most of these additives dissolve relatively equally well in the exposed and unexposed regions. In addition, most of these additives are relatively volatile liquids which escape into the atmosphere during the post exposure delay; therefore, photoresists containing these amine compounds have poor reproducibility. Furthermore, since these amine compounds are volatile, it is difficult to control the precise amount of these additives present in the photoresist during a photolithography process.
Therefore, there is a need for a photoresist additive compound which overcomes the above-mentioned disadvantages.
It is therefore an object of the present invention to provide an additive compound which improves the PED stability of photoresist compositions.
It is also an object of the present invention to provide a photoresist composition comprising the aforementioned additive.
In order to achieve the above-described objectives, the present invention provides urea derivatives that can improve PED stability of a photoresist by efficiently preventing the acid generated at an exposed region from reacting with environmental amine compounds.